Remove unused dependencies

[aniketnk]

Is your feature request related to a problem? Please describe.
There are many ununsed dependencies from package.json. Add them only as necessary.
Used the depcheck library to find them.

$ depcheck
Unused dependencies
* errorhandler
* nodemailer
* nodemailer-express-handlebars
Unused devDependencies
* @types/errorhandler
* @types/node
* @types/shelljs
* eslint-config-prettier
* eslint-config-strongloop
* eslint-plugin-prettier
* shelljs
* ts-node

Describe the solution you'd like
Use depcheck and remove unnecessary packages.

Describe alternatives you've considered
None

Additional context
Add any other context or screenshots about the feature request here.

[aniketnk]

Should apply to boilerplate once #1 is merged.

[aniketnk]

@temanisparsh What's the status on this?

[temanisparsh]

Will push changes in a while